This invention relates generally to improvements in infusion pumps such as those used for controlled delivery of fluid to a user. More specifically, this invention relates to improved methods and apparatuses for detecting fluid pressure and occlusions in fluid delivery paths of infusion pump systems.
Infusion pump devices and systems are relatively well-known in the medical arts, for use in delivering or dispensing a prescribed medication such as insulin to a patient. In one form, such devices comprise a relatively compact pump housing adapted to receive a syringe or reservoir carrying a prescribed medication for administration to the patient through infusion tubing and an associated catheter or infusion set.
A typical infusion pump includes a housing, which encloses a pump drive system, a fluid containment assembly, electronics system, and a power supply. The pump drive system typically includes a small motor (DC, stepper, solenoid, or other varieties) and drive train components such as gears, screws, and levers that convert rotational motor motion to a translational displacement of a stopper in a reservoir. The fluid containment assembly typically includes the reservoir with the stopper, tubing, and a catheter or infusion set to create a fluid path for carrying medication from the reservoir to the body of a user. The electronics system regulates power from the power supply to the motor. The electronics system may include programmable controls to operate the motor continuously or at periodic intervals to obtain a closely controlled and accurate delivery of the medication over an extended period. Such pump drive systems are utilized to administer insulin and other medications, with exemplary pump constructions being shown and described in U.S. Pat. Nos. 4,562,751; 4,678,408; 4,685,903; 5,080,653 and 5,097,122, which are incorporated by reference herein.
Infusion pumps of the general type described above have provided significant advantages and benefits with respect to accurate and timely delivery of medication or other fluids over an extended period compared to manual syringe therapy. The infusion pump can be designed to be extremely compact as well as water resistant, and may be adapted to be carried by the user, for example, by means of a belt clip or a harness. As a result, precise amounts of medication may be automatically delivered to the user without significant restriction on the user""s mobility or life-style, including in some cases the ability to participate in water sports.
In the past, medication infusion pump drive systems have included alarm systems designed to detect and indicate a pump malfunction and/or non-delivery of the medication to the patient due to a fluid path occlusion. Such alarm systems have typically used a limit switch to detect when the force applied to the reservoir stopper reaches a set point. One known detector uses an xe2x80x9con/offxe2x80x9d limit switch. When a set point is reached, the switch changes state (from open to closed or visa versa) triggering an alarm to warn the user. In U.S. Pat. No. 4,562,751, the limit switch is positioned at one end of a rotatable lead screw. The force applied to the limit switch by the lead screw is proportional to the pressure applied to the medication as a result of power supplied to the drive system to advance the stopper.
When an occlusion develops in the fluid path, the first consequence is the lack of medication delivery, or xe2x80x9cunder-dosing.xe2x80x9d But, a potentially much greater danger arises from xe2x80x9cover-dosingxe2x80x9d due to an occlusion breaking free after pressure has built up in the fluid path. For example, if a drive system continues to receive commands to deliver medication when the fluid path is blocked, fluid pressure may continue to grow until the occlusion is forced out, which then causes a lot or the previously commanded medication to be expelled at once under pressure. This could result in an xe2x80x9cover dose.xe2x80x9d Thus, early detection of an occlusion minimizes the potential for xe2x80x9cover-dosing.xe2x80x9d
However, the use of an on/off limit switch as an occlusion detector has several disadvantages. The lead screw or other drive mechanism generally moves axially some distance to actuate the limit switch. If the medication is highly concentrated, and small incremental deliveries are required, such as 0.5 micro liters, then the required stopper displacement per delivery is very small. When an occlusion develops, the lead screw displacement toward the limit switch is also small. Therefore, many deliveries may be missed before the lead screw is displaced sufficiently to actuate the limit switch.
Additionally, a limit switch typically has only one set point. Noise, temporary pressure fluctuations during a delivery, and temperature and/or humidity effects may trigger false occlusion alarms. If the set point were placed higher to avoid some of the false detections, additional time would be required to detect a genuine occlusion.
According to an embodiment of the invention, an occlusion detection system for detecting an occlusion in a fluid path of an infusion pump with a reservoir containing fluid for delivering fluid to a user includes a housing, a motor, a reservoir, one or more drive train components, a sensor, and an electronics system. The motor is contained within the housing, and the one or more drive train components react to stimulus from the motor to force fluid from a reservoir into the user. The sensor is positioned to measure a parameter associated with the motor or a drive train component, and the sensor produces three or more output levels across a range of measurements. The electronics system processes the three or more sensor output levels to declare when an occlusion exists.
In preferred embodiments, the sensor measures a force proportional to a force applied to a drive train component. In particular embodiments, the drive train component is a lead screw. In other particular embodiments, the drive train component is a slide.
In alternative embodiments, the sensor measures tension or compression on a beam proportional to a torque applied to the motor. In particular embodiments, the drive train component is a beam. In other particular embodiments, the drive train component is one or more mounts.
In other alternative embodiments, the sensor measures tension or compression proportional to a pressure applied to a drive train component. In particular embodiments, the drive train component is a bellows. In other particular embodiments the drive train component is a cap.
In preferred embodiments, the sensor is a force sensitive resistor. In alternative embodiments, the sensor is a capacitive sensor. In other alternative embodiments, the sensor is a strain gauge. In still other alternative embodiments the sensor is a piezoelectric sensor.
In preferred embodiments, the electronics system uses a maximum measurement threshold method to declare when an occlusion exists. In particular embodiments, a measurement threshold is at least 2.00 pounds.
In alternative embodiments, the electronics system uses a slope threshold method to declare when an occlusion exists. In particular embodiments, a slope threshold is about 0.05 pounds per measurement.
In other alternative embodiments, the electronics system uses a maximum measurement threshold method, and a slope threshold method to declare when an occlusion exists. In still other alternative embodiments, one or more measurements must exceed a minimum level to declare that an occlusion exists.
In preferred embodiments, the measured parameter is correlated with a fluid pressure in the reservoir. In particular embodiments, the electronics system processes the sensor output levels to determine when the reservoir is empty. In other particular embodiments, the electronics system processes the sensor output levels to determine when a stopper contacts an end of the reservoir. In still other particular embodiments, the electronics system processes the sensor output levels to determine when a slide is seated in a stopper.
In preferred embodiments, the sensor is positioned between the motor and a housing component. In particular embodiments, VHB adhesive is positioned between the motor and the housing component. In other particular embodiments, one or more components including the sensor are stacked between the motor and the housing component, and the housing component is positioned to remove space between the one or more components before the housing component is attached to the housing. In alternative embodiments, one or more components including the sensor are stacked between the motor and the housing, and back-fill material is injected through the housing to remove space between the one or more components and to fill the space between the one or more components and the housing.
According to an embodiment of the invention, a method of detecting an occlusion in an infusion pump for infusing fluid into the body of a user includes the steps of obtaining a measurement from a sensor before each fluid delivery, calculating a slope of a line generated using two or more measurements, comparing the slope to a slope threshold, incrementing a counter when the slope exceeds the slope threshold, and declaring an occlusion when the counter exceeds a detection count
According to another embodiment of the invention, a method of detecting an occlusion in an infusion pump for infusing fluid into the body of a user includes the steps of obtaining a measurement from a sensor before each fluid delivery, calculating a current slope of a line using two or more measurements, calculating an average slope using a previous average slope and the current slope, comparing the average slope to a slope threshold, incrementing a counter when the average slope exceeds the slope threshold, and declaring an occlusion when the counter exceeds a detection count value. In preferred embodiments, the two or more measurements are not consecutive.
According to another embodiment of the invention, an occlusion detection system for detecting an occlusion in a fluid path of an infusion pump with a reservoir containing fluid for delivering fluid to a user includes, a housing, forcing means for forcing fluid from a reservoir containing a fluid, sensing means for sensing a parameter associated with the forcing means for forcing fluid from the reservoir containing the fluid to obtain one or more measurements, and evaluation means. The sensing means producing one of three or more output levels for each of the one or more the measurements. The evaluation means evaluates the one of three or more output levels associated with each of the one or more measurements to declare when an occlusion exists.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, various features of embodiments of the invention.